1. Field of the Invention
The present invention relates to a speed-change hub for use in e.g. a bicycle, and more particularly to a speed-change hub including a fixed shaft, a hub body rotatably mounted on the fixed shaft, a drive member rotatably mounted on the fixed shaft for transmitting a drive force to the hub body selectively through a plurality of transmission channels and a clutch for selecting one of the transmission channels.
2. Description of the Related Art
A known speed-change hub of the above-specified type includes first and second sun gears rotatable relative to a fixed shaft and having different diameters and a lock control mechanism for locking the sun gears to and releasing the same from the fixed shaft. The fixed shaft further includes an axially movable first control portion having a control portion for controlling a clutch element and externally operable at one distal end of the hub body and an axially movable second control portion having a control portion for activating the lock control mechanism to lock either the first or second sun gear to the fixed shaft. Accordingly, by moving the first control portion, the clutch is operated to select a desired transmission channel. Also, by moving the second control portion, one of the first and second sun gears is locked to the fixed shaft. In this way, the hub provides a plurality of speeds (Japanese published patent gazette No. 53-14820).
Recently, the prior art has suggested a further type of speed-change hub having only one one control portion (West Germany laid-open patent gazette No. 2458871). With this speed-change hub, the control portion is rotated to axially move a sun gear and a planet gear meshing therewith.
One problem occurs with the above speed-change hub however. That is, since the speed-changing operation is effected by operating the sun gear and the planet gear which are being rotated in union (more particularly, the planet gear, the sun gear and also the hub body are acting on each other), the control portion tends to be subjected to a relatively large load which results in a `heavy` speed-change operation feel. In this sense, this speed-change hub still has room for improvement.
The present invention attends to the abovedescribed drawback of the prior art. Hence, the invention's primary object is to provide an improved speed-change hub which provides a light speed-changing operation feel to the user because of an effectively reduced load acting on the control portion of the hub.